Superabsorbent polymers

Abstract

Superabsorbent, high gel strength/short gel time acrylic polymers, well suited for the production of items of feminine hygiene/adult incontinence, are prepared by (a) inversely suspending an aqueous acrylic monomer phase in an organic solvent in the presence of an emulsifying agent having an HLB of from 8 to 12, the aqueous monomer phase also comprising a crosslinking agent therefor, (b) polymerizing the inverse suspension of acrylic monomer into a polymer gel, (c) absorbing a second charge of acrylic monomer into the polymer gel thus attained, the ratio of the amount of the second monomer charge to the amount of monomer in the beginning aqueous phase ranging from 1 to 1.2, (d) introducing a surfactant having an HLB of from 2 to 5 into the medium of polymerization, and (e) polymerizing the second monomer charge within the polymer gel.

What is claimed is: 
     
       1. A process for the preparation of a superabsorbent acrylic polymer having (i) a gelling time ranging from 15 to 40 seconds, (ii) a gel strength of more than 2,800 Pascals, (iii) capillary action/suction under 2 kPa of more than 30 ml/g. (iv) capillary action/suction under 5 kPa of more than 20 ml/g, (v) an absorption capacity in excess of 50 g/g, (iv) a content of extractables of less than 10%, (vii) a content of fines of less than 10%, and (viii) a retention of greater than 28 g/g, which comprises (a) inversely suspending an aqueous acrylic monomer phase in an organic solvent in the presence of an emulsifying agent having an HLB of from 8 to 12, said aqueous monomer phase also comprising a crosslinking agent therefor, (b) polymerizing said inverse suspension of acrylic monomer into a polymer gel, (c) absorbing a second charge of acrylic monomer into the polymer gel thus attained, the ratio of the amount of said second monomer charge to the amount of monomer in said beginning aqueous phase ranging from 1 to 1.2, thereafter (d) introducing a surfactant having an HLB of from 2 to 5 into the medium of polymerization, and subsequently (e) polymerizing said second monomer charge within said polymer gel. 
     
     
       2. The process as defined by claim 1, said surfactant having an HLB of from 2 to 5 comprising sucrose di/tristearate. 
     
     
       3. The process as defined by claim 1, said crosslinking agent comprising a bisacrylic compound or a diglycidyl ether. 
     
     
       4. The process as defined by claim 3, said crosslinking agent comprising ethylene glycol diglycidyl ether. 
     
     
       5. The process as defined by claim 1, said crosslinking agent comprising N,N-methylenebisacrylamide. 
     
     
       6. The process as defined by claim 1, wherein the ratio by weight of said beginning aqueous phase to said organic solvent ranges from 0.7 to 1.1. 
     
     
       7. The process as defined by claim 1, said second monomer charge also comprising a crosslinking agent therefor.